1. Field of the Present Invention
The present invention relates to a method for manufacturing a bonded optical disc that records information and comprises a plurality of disc substrates bonded together, such as a DVD.
2. Description of the Related Art
Disc-shaped recording media (optical discs) on which information is recorded and played back by irradiating the optical disc with a laser, such as compact discs (CD-ROMs), recordable compact disc (CD-Rs), digital versatile discs (DVD-ROMs), recordable DVD (DVD-Rs), and rewritable DVD (DVD-RWs), are well known. Optical discs such as DVD-ROMs, DVD-Rs, and DVD-RWs, on which information is recorded at a high density, typically comprise a plurality of disc substrates (normally two) bonded together by an adhesive or the like.
DVD-ROMs, DVD-Rs, and DVD-RWs must be manufactured with high dimensional accuracy because they have an extremely small range of dimensional error allowance with respect to radial-direction warping and circumferential-direction runout.
An example of a method for manufacturing this type of optical disc is shown in FIG. 3A. A coating solution comprising an organic colorant is coated onto the surface of a substrate 50, which is formed by injection molding or the like, and dried (heated) to form a recording layer 52. After the formation of the recording layer, a reflective layer and a protective layer or the like (not shown) are formed. Then, as shown in FIGS. 3B and 3C, a dummy substrate 54 is bonded to the substrate 50.
In this method, heating the substrate 50 disposed with the recording layer 52 causes slight warping of the substrate 50 (i.e., there is a tendency for the recording layer 52 to stretch and for the substrate 50 to shrink). However, since the dummy substrate 54 is not warped because it is not heated (see FIGS. 3A and 3B), slight warping in a resultant optical disc 56 occurs when the dummy substrate 54 is adhered to the recording layer 54 (see FIG. 3C).
The present invention has been developed taking the foregoing problem into consideration, and an object thereof is to provide a method for manufacturing a bonded optical disc in which warping of the optical disc is substantially eliminated.
The present invention provides a method for manufacturing a bonded optical disc comprising the steps of: coating a solution on a substrate; heating the coated substrate to thereby form a recording layer on the substrate; and adhering a dummy substrate to the recording layer, wherein the dummy substrate is also heated.